1. Field of the Invention
The present invention relates to a liquid-crystal coating fluid and a polarizing film made therefrom.
2. Description of the Related Art
A polarizing plate obtained by dying a resin film, such as a polyvinyl alcohol or the like with iodine or a dichromatic dye and stretching the film in one direction has been widely used as a polarizing plate for a liquid crystal panel. However, there has been a problem that the aforementioned polarizing plate is poor in heat resistance and light resistance depending on the kind of the dye or the resin film. Moreover, film manufacturing equipment has become bigger as liquid crystal panels become bigger, which has become a problem.
In contrast, a method for forming a polarizing film by casting a liquid-crystal coating fluid containing a lyotropic liquid crystal compound on a substrate, such as a glass plate or a resin film and the like to orient the lyotropic liquid crystal compound is known.
The lyotropic liquid crystal compound forms supramolecular aggregates exhibiting liquid crystallinity in the solution, so that the long axis direction of the supramolecular aggregates is oriented in a flowing direction when flowing after applying shearing stress onto the liquid-crystal coating fluid containing this.
Examples of such lyotropic liquid crystal compounds include azo compounds (JP 2006-323377 A). Lyotropic liquid crystal compounds based polarizing films do not need to be stretched. In addition, it is possible to reduce the thickness of the polarizing films significantly. Further, the lyotropic liquid crystal compounds based polarizing films are expected to have potential because the thickness can be reduced significantly.
However, the polarizing film obtained by casting a liquid-crystal coating fluid including a conventional azo compound has a drawback that fine crystals are separated out in the film in a drying process, so that transparency is deteriorated due to an increase in haze (light scattering) of the polarizing film. Thus, a liquid-crystal coating fluid including a novel azo compound which has resolved this problem has been needed.